Known for her terrifying smile that fuels superstitions, Miroku, the slit-mouthed woman, surprisingly has a fiancé. Once a prominent urban legend, she faces a crisis as people stop believing in her existence. Forced into a contractual marriage with Kouichi Sano, a 17-year-old from a family tied to the supernatural world, Miroku is determined to reclaim her fame. Sano challenges her: if she can scare him before his 18th birthday, he will annul the engagement. However, Miroku is taken aback by his countercondition—to make her fall in love with him.